Fix #993 - create class string from reconciled assertions where necessary

src/Psalm/Type/Reconciler.php

@@ -1450,6 +1450,10 @@ class Reconciler
             }
         } elseif ($scalar_type === 'string' || $scalar_type === 'class-string') {
             if ($existing_var_type->isMixed()) {
+                if ($scalar_type === 'class-string') {
+                    return new Type\Union([new Type\Atomic\TLiteralClassString($value)]);
+                }
+
                 return new Type\Union([new Type\Atomic\TLiteralString($value)]);
             }
 

tests/ClassStringTest.php

@@ -260,6 +260,24 @@ class ClassStringTest extends TestCase
                         if ($class === A::class) {}
                     }',
             ],
+            'switchMixedVar' => [
+                '<?php
+                    class A {}
+                    class B {}
+                    class C {}
+
+                    /** @param mixed $a */
+                    function foo($a) : void {
+                        switch ($a) {
+                            case A::class:
+                                return;
+                          
+                            case B::class:
+                            case C::class:
+                                return;
+                        }
+                    }',
+            ],
         ];
     }